The present invention relates to a catalytic hydrocarbon conversion, and, in particular, to catalytic dewaxing processes carried out in the presence of crystalline zeolitic material.
It has been known in art of petroleum processing to reduce the pour point of hydrocarbon oils by reducing those hydrocarbons which readily solidify (waxes) from the hydrocarbon feedstock. Previously, waxy components had been removed by means of low temperature solvent extraction. More recently, however, catalytic techniques have been made available for dewaxing petroleum feedstocks.
A process of that nature developed by British Petroleum is described in The Oil and Gas Journal dated Jan. 6, 1975, at pages 69-73. See also U.S. Pat. No. 3,668,113.
In U.S. Pat. No. Re. 28,398 to Chen et al. a process for catalytic dewaxing is described using with a catalyst comprising zeolite ZSM-5.
U.S. Pat. No. 3,956,102 is connected with a process involving the hydrodewaxing of petroleum distillates utilizing a ZSM-5 zeolite catalyst.
U.S. Pat. No. 4,247,388 to Banta, et al. discloses that the catalytic performance of certain acidic zeolites such as those of the ZSM-5 type in hydrodewaxing operations is improved by controlling the alpha activity of such zeolites to within the range of 55-150, e.g., by treatment with steam.
U.S. Pat. No. 4,284,529 to Shihabi discloses improvements in pour point reduction by means of catalytic dewaxing employing a catalyst prepared from a ZSM-5 type zeolite having a constraint index of about 1 to 12. This dewaxing process employs a low acidity form of zeolite such as ZSM-5 or ZSM-11 in which the low acidity is imparted by steaming the zeolite to reduce its cracking activity to an alpha value of not less than about 5, followed by base ion exchange with an alkali metal cation to reduce the alpha value to no greater than 1.0. A preferred catalyst is referred to therein as a pre-steamed NaZSM-5 and is employed to dewax crude oils and other waxy feedstocks in the presence or absence of added hydrogen. These catalysts are effective at start-of-run temperature of about 640.degree. F. and exhibit excellent aging behavior in the presence of hydrogen. However, in the absence of hydrogen these catalysts exhibit a gradual aging requiring a daily increase of about 1.degree.-10.degree. F. in the reaction temperature.
U.S. Pat. No. 4,448,673 to Shihabi describes a high silica-to-alumina ratio acidic crystalline zeolite catalyst of a group, which includes ZSM-5, having increased activity. The zeolite catalyst is prepared by steaming a precursor crystalline aluminosilicate in the hydrogen or ammonium form which has an alpha valve of greater than about 20 in the presence of ammonia to provide a crystalline alluminosilicate having an alpha value of from about 10 to about 150 and thereafter ion-exchanging the steamed precursor with an alkali metal cation under conditions effective to further reduce the alpha value to less than about 10.
U.S. Pat. No. 4,510,045 to Dessau discloses a hydrodewaxing process which includes use of an non-acidic medium pore zeolite, such as ZSM-5, activated by steaming in the presence of binders such as alumina.
Catalytic dewaxing as produced today involves shape selective conversion of straight and slightly branched aliphatic compounds of 12 or more carbon atoms. Such conversion includes cracking the paraffinic components, which can reduce the yield of product having acceptable pour point because of loss of low carbon chains resulting from the cracking. Reduction of the waxy component can also result from isomerization of the paraffin chains, which does not effect the overall yield of acceptable product.
This latter dewaxing activity has been known to occur in the case of large pore zeolites. However, large pore zeolites are particularly susceptible to poisoning, such as by nitrogen and thus can require unacceptably high temperature processing to minimize the effect of such poisoning.
As a result of the present invention, however, these and other problems associated with dewaxing of hydrocarbon feedstocks, especially those containing a relatively high content of poisonous compounds such as nitrogen as well as a waxy component have been mitigated.